UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
4 results
Search Results
Item Nitrogen dynamics in cover crop-based no-till corn(2014) Poffenbarger, Hanna Jane; Weil, Ray R; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Legume/grass cover crop mixtures and sidedress subsurface band manure application are two approaches to improving nitrogen (N) use efficiency in a cover crop-based no-till corn (Zea mays L.) system. The objectives of this study were to: 1) quantify cover crop biomass and N content in response to different hairy vetch (Vicia villosa Roth)/cereal rye (Secale cereale L.) sown proportions, 2) evaluate the effects of cover crop species proportions and pelletized poultry litter (PPL) application method on residue decomposition, and 3) model the spatio-temporal dynamics of soil inorganic N as influenced by different cover crop residues and subsurface band-applied PPL. Results suggest that cover crop mixtures can accumulate as much biomass as a cereal rye monoculture and as much N as a hairy vetch monoculture, and have decomposition patterns intermediate between those of monocultures. Subsurface band PPL application provided a localized N source that did not influence decomposition of surface mulches.Item Linking detritus and primary producer based communities(2008-03-25) Hines, Jessica; Denno, Robert F; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Terrestrial food-web theory has been developed largely by examining species interactions in primary producer food webs. However, the decomposer subsystem can have strong influences on aboveground communities and ecosystem functioning. Here I examine, at several spatial scales, the complexity of terrestrial food-web interactions by considering interactions between species in detritivore and primary-producer food webs. I focused on Spartina alterniflora marshes and interactions among the numerically dominant herbivore Prokelisia dolus, its major spider predator Pardosa littoralis, and several detritivores (Littorophiloscia vittata, Orchestia grillus, Melampus bidentatus and Littoraria irrorata). I found that predator-detritivore interactions have weak indirect effects on plant growth and decomposition (Chapter 1). Furthermore, by serving as alternative prey, detritivores can influence the strength of predator-herbivore interactions. However, the strength of predator-herbivore-detritivore interactions was species-specific and depended on habitat structure (leaf litter - Chapter 1) and detritivore identity (Chapter 2). Although detritivore species are often functionally redundant in soil communities, changes in detritivore species composition can have divergent influences on aboveground predator-herbivore interactions (Chapter 2). Whereas some detritivores (Littorophiloscia vittatta) promote herbivore and predator survival, other detritivores (Littoraria irroratta) reduce predator and herbivore densities. Moreover, the geographic distribution of detritivores influences the relative strength of predator-herbivore interactions across broader spatial scales (Chapter 3). I found a shift in the relative abundance of dominant detritivore, herbivore, and predator species across a 1660 km latitudinal gradient. Detritivorous Littoraria snails that abound on low-latitude marshes modify Spartina vegetation structure and create an unfavorable habitat for Pardosa spiders. Pardosa exert stronger predation pressure on Prokelisia planthoppers on high-latitude marshes where spiders are abundant. Changes in global carbon cycles may influence the strength of linkages between primary production and decomposition food webs. I examined how changes in the detritivore food chain influenced the growth of two plant species (Scirpus olneyi and Spartina patens) under elevated and ambient CO2 conditions. I found limited and species-specific support for the increased importance of the decomposition pathway under elevated CO2 conditions. Overall, detritivores modified predator-herbivore interactions, live plant growth, and decomposition. The strength of these interactions changed with the composition of the detritivore community, latitude, and atmospheric CO2 conditions.Item Changes in the Wage Gap of Gender and Caste Groups in India(2006-04-24) Jacob, Marilyn; Sanders, Seth; Economics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We explore the changes in the wage gap of caste and gender groups in India. Traditional Hindu society divided people into social classes based on the caste system. The lowest of the castes have traditionally been economically disadvantaged. Women in India have typically been restricted to the household and their participation in the formal labor market has begun expanding only recently. We explore the changes that these two groups have experienced over the years using a nationally representative dataset. In the second chapter we decompose the wage gaps of these groups into explained and unexplained components based on the Blinder-Oaxaca (1973) decomposition technique. Our contribution to the literature here is the extension of the analysis of discrimination to a society with a clearly established social hierarchy. We find that the gross wage gap has reduced over this period, and the extent of the gap attributable to discrimination has decreased over time. We further decompose the wage gap into components attributable to wage differences and occupational differences based on Brown et al. (1980). We find that the wage discrimination component has decreased over time and the job discrimination component is statistically insignificant. In the third chapter we investigate whether there have been beneficial wage gains for women and lower castes because of increased competition following liberalization of trade in India. Based on Becker's model of taste-based employer discrimination, it is expected that as an economy becomes more competitive, employer discrimination should decline. The trade liberalization reforms that began in 1991 in India increased competition by lowering protection in certain manufacturing industries. Firms who could indulge a taste for discrimination when trade protection allowed supernormal profits may not have been able to continue to do so as competition eliminated such profits. Using individual-level data and tariff data from pre- and post-reform periods, we find that wage differences reduced for female workers relative to male workers in the more open manufacturing sector industries. However, there is no significant effect on the wage differential between low and high caste workers.Item MULTIOBJECTIVE OPTIMIZATION MODELS AND SOLUTION METHODS FOR PLANNING LAND DEVELOPMENT USING MINIMUM SPANNING TREES, LAGRANGIAN RELAXATION AND DECOMPOSITION TECHNIQUES(2005-08-04) Faria, Jose Alberto; Gabriel, Steven A; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The land development problem is presented as the optimization of a weighted average of the objectives of three or more stakeholders, subject to develop within bounds residential, industrial and commercial areas that meet governmental goals. The work is broken into three main sections. First, a mixed integer formulation of the problem is presented along with an algorithm based on decomposition techniques that numerically has proven to outperform other solution methods. Second, a quadratic mixed integer programming formulation is presented including a compactness measure as applied to land development. Finally, to prevent the proliferation of sprawl a new measure of compactness that involves the use of the minimum spanning tree is embedded into a mixed integer programming formulation. Despite the exponential number of variables and constraints required to define the minimum spanning tree, this problem was solved using a hybrid algorithm developed in this research.